Musical-tone-waveform forming apparatus for an electronic musical instrument

Abstract

An apparatus for forming a musical-tone waveform for an electronic musical instrument characterized in that at least one cycle of a musical-tone waveform, which it is desired be produced, is divided in amplitude by dividing lines at equal intervals and sampling points on a time axis are determined from respective crossing points between the waveform and the dividing lines and the distance between the initial and the final sampling points is represented by an appropriate number of pulses so that each sampling point may be represented by a pulse number. There is further provided a memory circuit wherein each sampling point, that is, the pulse number thereof is set up in the form of a digital signal. Additionally, there is a set up in the form of a digital signal a tendency such as increase, decrease or equal at each sampling point with reference to the preceding sampling point. An envelope setting device is used wherein the envelope of a muscial-tone waveform, which it is desired be produced, is subjected to sampling and the analog amount of each sampling point is set up in the form of digital signal. An accumulatively adding device is employed whereby the output digital signal of the envelope setting device is accumulatively added to or subtracted from the output digital signal of the memory circuit. The accumulatively adding device is connected at its output terminal to a D-A converter for converting its output signal into an analog signal.

What is claimed is: 
     
       1. Apparatus for forming a musical-tone waveform for an electronic musical instrument, at least one cycle of said musical-tone waveform being divided in amplitude by dividing lines spaced at equal intervals, sampling points on time axis being determined from respective crossing points between the waveform and the dividing lines, distance between initial and final of the sampling points being represented as a number of pulses such that each sampling point can be represented by a pulse number, said waveform at each sampling point having an increase, decrease or equal tendency, said apparatus comprising memory means wherein the pulse number of each sampling point is set up in the form of a digital signal and wherein additionally said tendency is set up in the form of a digital signal, envelope setting means wherein an envelope of said musical-tone waveform is subjected to sampling and the analog amount of each sampling point is set up in the form of a digital signal, and accumulatively adding means wherein an output digital signal of the envelope setting means is accumulatively added to or subtracted from an output digital signal of said memory means and a D-A converter means, said accumulatively adding means being connected at its output to said D-A converter means for converting output signals into analog signals. 
     
     
       2. An apparatus as claimed in claim 1, wherein the said memory means includes at least two portions each adapted for the setting up of increase, decrease and equal tendencies of a waveform, and a calculation circuit means controlled by outputs of said two portions, said apparatus further including multiplier means, the output of the calculation circuit means and the output of the envelope setting means being multiplied by one another by said multiplier means and the resulting output thereof being applied to the said accumulatively adding means. 
     
     
       3. An apparatus as claimed in claim 1 wherein the accumulatively adding means comprises a plurality of AND circuits, exclusive-OR circuits, full adders and latch circuits coupled in operative association. 
     
     
       4. An apparatus as claimed in claim 1 comprising a clock pulse generator, a coincidence circuit coupled to said clock pulse generator, and a decoder, and wherein said memory means comprises a read-only memory, having a plurality of output terminals and a counter having a plurality of output terminals for counting output pulses of said clock pulse generator and connected to a coincidence circuit, the output of the coincidence circuit being connected to said decoder for designating addresses in the read-only memory and to said accumulatively adding device. 
     
     
       5. An apparatus as claimed in claim 1 comprising a decoder and a pulse oscillator and wherein the envelope setting means comprises a read-only memory, having an input connected to said decoder which is driven by output pulses of said pulse oscillator and designates addresses in order. 
     
     
       6. An apparatus as claimed in claim 1 wherein said memory means includes a single ring counter. 
     
     
       7. An apparatus as claimed in claim 2 wherein the accumulatively adding means comprises a plurality of AND circuits, exclusive-OR circuits, full adders and latch circuits coupled in operative association. 
     
     
       8. An apparatus as claimed in claim 2 comprising a clock pulse generator, a coincidence circuit coupled to said clock pulse generator, and a decoder, and wherein said memory means comprises a read-only memory, having a plurality of output terminals and a counter having a plurality of output terminals for counting output pulses of said clock pulse generator and connected to a coincidence circuit, the output of the coincidence circuit being connected to said decoder for designating addresses in the read-only memory and to said accumulatively adding device. 
     
     
       9. An apparatus as claimed in claim 2 comprising a decoder and a pulse oscillator and wherein the envelope setting means comprises a read-only memory, having an input connected to said decoder which is driven by output pulses of said pulse oscillator and designates addresses in order. 
     
     
       10. An apparatus as claimed in claim 4, wherein the said counter includes a programmable counter that is automatically reset when one cycle of the musical tone waveform is concluded. 
     
     
       11. An apparatus as claimed in claim 4, wherein the said counter includes means to be reset by an output signal of the coincidence circuit whereby the number of bits required in the memory means is decreased. 
     
     
       12. A method for forming a cycle of a musical-tone waveform comprising intersecting with the waveform of said cycle equally spaced amplitude dividing lines, representing the time extent of said cycle by a sequence of regularly spaced pulses, representing intersections between said lines and waveform by respective pulses having respective numbers in said sequence, and identifying at each intersection the tendency of the waveform to increase, decrease or remain constant in amplitude, storing the pulse numbers and tendencies as available information, and reconstructing the waveform from said information. 
     
     
       13. A method as claimed in claim 12 comprising storing the information in the form of digital signals. 
     
     
       14. A method as claimed in claim 13 comprising reconstructing the waveform by a digital to analog conversion based on said digital signals.